The most significant decision of Bill Belichick’s career was sticking with backup quarterback Tom Brady, who emerged following an injury to Patriots starter Drew Bledsoe, in 2001. Bledsoe spent the rest of the season as the backup to Brady, and after New England won the Super Bowl behind him, the thirty-year-old Bledsoe was traded for a first-round draft pick to the Buffalo Bills. Brady went on to win three more Super Bowls, appear in two others, and played about as well as a quarterback can play as recently as this week, completing 82.9 percent of his passes for 376 yards and three touchdowns against a good Bengals defense.

Bledsoe was a popular, face-of-the-franchise player with the Patriots for eight years. But he finished his career in Dallas, where he was eventually replaced during the 2006 season by another unexpected backup: an undrafted free agent quarterback named Tony Romo.

Life comes full circle, and the past several weeks have proven that. This time, it’s Romo who—thanks to a back injury—has been supplanted by an upstart QB who was not expected to be anybody’s starter just a few months ago. Cowboys fans are wearing Dak Prescott jerseys these days, and even though Tony Romo is one of the more beloved and iconic Cowboys in recent memory, his time with the team seems to be at its end.

Romo, throughout his career, has been a genuine star quarterback. When healthy, he’s easily been among the league’s best. The ill-timed interceptions have overshadowed some of his greatness, but he’s spent much of his career carrying the team on his (often injured) back with ease. But Romo is 36. Dak Prescott is winning football games and looking great while doing it. And Romo’s annual salary of $18 million is only $7 million shy of what it takes to (say) buy a beloved statewide magazine. Prescott’s annual salary is $450,000.

Jerry Jones has managed to dodge the question of whether Romo will be back. When asked after the Cowboys effectively dismantled the Green Bay Packers on Sunday, Jones responded, “I wouldn’t say unequivocally anything—other than we just beat the Green Bay Packers in Green Bay.” But regardless of if the Cowboys pull Prescott for Romo when the starter has recovered enough from his previous injury to suffer his next one, the future quarterback of the Cowboys organization is named Dak, not Tony. The question of what to do with Romo when he’s healthy lingers—he was expected to return in week nine, though the Cowboys currently operating on a “100 percent healthy” timetable, which is probably something Romo will never enjoy again in his life (even without a history of back injuries, who in their mid- to late-thirties or beyond can claim to be 100 percent healthy?)—but barring a befuddling decision from Jones, the Cowboys’ starter in 2017 will be Dak Prescott.

So what to do with Tony Romo? He’ll be 37 at the start of the 2017 season. He’ll have been 15-3 in his last regular season starts. He’ll have a long injury history, and, assuming a full recovery from his most recent injury, which does not appear to be in question, he’ll still probably be one of the best quarterbacks in football. Keeping him in Dallas would be bizarre—nobody pays $18 million a year to their backup, and wasting a year of Prescott at his bargain-basement salary is not how successful NFL franchises operate. The question, then, is what sort of trade value does Tony Romo have?

It’s worth noting that, when assessing the question this way, the difference between Romo and Prescott becomes obvious. Romo, if he were to be available, would be worth consideration from maybe a half-dozen teams in the NFL who both need help at QB and are close enough to competing that he’d make sense as an acquisition. There are probably at least twenty NFL teams who would trade their current starting quarterback and a draft pick or two to the Cowboys for Prescott—and Jones would be a fool to even entertain those offers.

There isn’t an abundance of recent comparisons to a star quarterback in the twilight of his career hitting the trade block, but you could look at the aforementioned Bledsoe. Bledsoe was traded for a first-round pick in 2001, but he was 29-years-old and his long-term health was not a serious question. More recently, former Cincinnati Bengals quarterback Carson Palmer was traded to the Oakland Raiders in 2011 for a first-round pick and a conditional second-rounder in the middle of the season. That deal didn’t exactly work out for the Raiders, who flipped Palmer (who was 31 at the time) to the Arizona Cardinals two seasons later, turning those two high draft picks into an 8-15 record and a sixth rounder.

If Romo’s on the block, in other words, he’s probably on the block closer to the 2013 version of Carson Palmer than the 2011 version. Those high-profile trades for a quarterback seldom work out.

But sometimes they do, and that will probably inform the Romo talk. Earlier this year, after a preseason injury to starter Teddy Bridgewater, the Minnesota Vikings swapped a first-round draft pick for Sam Bradford, a marginal talent in his time with the Philadelphia Eagles (who had his replacement, second-overall pick Carson Wentz, already on the roster at the time Bridgewater suffered his injury). The move was widely derided at the time, but the Vikings knew what they were doing. Bradford has played the best ball of his career in Minnesota, and the organization is currently the only undefeated team left in the NFL.

Still, a Bradford-like deal for Romo seems unlikely. While Bradford had never played up to his potential in the past, he’s a 28-year-old former number-one overall pick, and the Vikings had circumstances that necessitated the trade. Namely, Bridgewater’s gruesome injury coming so late in the preseason, and a potent enough defense that the team had every reason to believe they’d be a legit contender with a competent QB. Those circumstances are unlikely to repeat—if Romo gets traded in the off-season, it won’t be the same sort of seller’s market that saw Palmer and Bradford command a premium.

The two best comparisons one could reasonably draw to an available Tony Romo, then, are two hall-of-famers who found themselves out of their franchises in favor of an heir apparent before they were ready to go: Brett Favre and Peyton Manning.

Favre played sixteen seasons with the Green Bay Packers, and following some serious waffling about retirement, stepped away from the team after the 2007 season at the age of 39. At that point, Aaron Rodgers—who had spent three years waiting for the chance to play—took over, and when Favre came out of retirement, the Packers opted to stick with the younger player. Favre was traded to the New York Jets for a conditional fourth round pick (which, had he excelled on the field, could have escalated to a first-rounder). Favre went 9-7 with the Jets, then retired again before being released and resurfacing as a free agent with the Vikings, where he came within a play in the NFC Championship Game of taking the team to the Super Bowl.

Manning, meanwhile, was never traded. It’s not because there wasn’t a market for his services—at the end of his career with the Indianapolis Colts in 2012, the quarterback, who was 36-years-old at the time he was cut, had a contract that would have left Indianapolis on the hook for more than $38 million in dead money. He was courted by teams from the Houston Texans to the New York Jets to the Denver Broncos, before eventually settling in Denver. He stayed for three seasons and led the team to the playoffs in his first season, losing in double-overtime, before two back-to-back Super Bowl appearances.

Manning’s health was no more a sure thing when he went to Denver than Romo’s is right now. Favre, who never missed a game in Green Bay, was much more steady a player, but no quarterback that close to 40 is a sure thing. Which means that, when teams consider Romo’s value, they’d probably assess him similar to how they assessed Manning or Favre.

With that in mind, it’s easy to imagine the sort of team that could be interested in Romo. It’d be a contender who’ll finish the 2016 season with a record that’s too good to earn a high draft pick next May, but which needs a quarterback to avoid squandering the sort of supporting talent that keeps them in the middle of the pack.

It’s early to make those sort of predictions, but they’re probably the same teams that were interested in Manning in 2012. The Texans, the Broncos, and the Jets are all competitive teams that, but for a quarterback they can believe in, look like real-deal competitors. Should they fall short in 2016, it’s easy to imagine a conditional fourth-round pick being a gamble they’re willing to make on Tony Romo. And the Cowboys, if they believe in equipping Dak Prescott for the bright future he seems to have ahead of him in Dallas, would be wise to take it.